I'm agnostic but skeptical about cosmological inflation. This preprint (which is part of a series of articles) is a middle ground between conventional cosmological inflation theory and a true no inflation theory.
Rather than a new substance/particle, it relies upon the quantum nature of space-time itself for its conclusions.
We present a complete computation of the scalar power spectrum in the inflation without inflaton (IWI) framework, where the inflationary expansion is driven solely by a de~Sitter (dS) background and scalar fluctuations arise as second-order effects sourced by tensor perturbations. By explicitly deriving and numerically integrating the full second-order kernel of the Einstein equations, we obtain a scale-invariant scalar spectrum without invoking a fundamental scalar field.
In this framework, the amplitude of the scalar fluctuations is directly linked to the scale of inflation. More precisely, we show that matching the observed level of scalar fluctuations, Δ2ϕ(k∗) ≈ 10^−9 at Cosmic Microwave Background (CMB) scales, fixes the inflationary energy scale H(inf) as a function of the number of observed e-folds N(obs).
For N(obs) ≃ 30 − 60, we find Hinf≃5×10^13 GeV − 2 × 10^10 GeV, corresponding to a tensor-to-scalar ratio r≃ 0.01 − 5 × 10^−9. In particular, requiring consistency with instantaneous reheating, we predict a number of e-folds of order~(50) and an inflationary scale H(inf) ≃ 10^11GeV. We also incorporate in our framework the quantum break-time of the dS state and show that it imposes an upper bound on the number of particle species. Specifically, using laboratory constraints on the number of species limits the duration of inflation to N(obs) ≲ 126 e-folds.
These results establish the IWI scenario as a predictive and falsifiable alternative to standard inflaton-driven models, linking the observed amplitude of primordial fluctuations directly to the quantum nature and finite lifetime of dS space.
Marisol Traforetti, et al., "Inflation without an Inflaton II: observational predictions" arXiv:2511.11808 (November 14, 2025).
what about the Higgs inflation since Higgs field exists? LQC has bounce scenarios that succeeds in inflation like results
ReplyDeleteThe basic concern I have is that it isn't clear that inflation is needed at all to solve the "problems" that it allegedly solved, and there is really no smoking gun positive evidence for it. Anything that inflation does can also be done by changing the initial conditions.
ReplyDeleteare those changing the initial conditions compatible with GR + SM?
ReplyDeleteYou just set the initial conditions to whatever they would have been immediately after inflation in an inflation theory. It doesn't even need to be at a volume of space = 0 state. Everything would flow exactly the same.
ReplyDeleteinflation theory in hybrid Loop Quantum Cosmology
ReplyDeletearXiv:2511.15553 (gr-qc)
[Submitted on 19 Nov 2025]
Starobinsky potential and power suppression in hybrid Loop Quantum Cosmology
Marceau Henry, Guillermo A. Mena Marugán, Antonio Vicente-Becerril
We study the effect on the primordial tensor power spectrum of varying the number of e-folds during slow-roll inflation in Loop Quantum Cosmology with a Starobinsky potential. Using the hybrid quantization approach, we derive the effective mass governing tensor mode evolution. The choice of vacuum state is crucial, especially since the preinflationary phase predicted by Loop Quantum Cosmology invalidates the choice of the Bunch-Davies state as the preferred vacuum. We adopt a choice which is optimally adapted to the dynamics, so that it provides a non-oscillating (NO) spectrum free of spurious contributions, and permits an asymptotic Hamiltonian diagonalization (AHD) of the perturbations. For this so-called NO-AHD vacuum, we compute the power spectrum using both analytic approximations and numerical integration. Our results confirm the accuracy of our approximations in a wide range of situations, including short- and long-lived inflationary scenarios. The primordial power spectrum exhibits a characteristic cutoff on a wavenumber scale determined primarily by the background dynamics around the bounce that replaces the big bang in Loop Quantum Cosmology.
Comments: 13 pages, 3 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
Cite as: arXiv:2511.15553 [gr-qc]